Most of the hypotheses that try to draw connections between subjective consciousness and physical events in the brain do so at the cellular level: that of individual neurons or neuronal assemblies. This approach—the search for the “neural correlates of consciousness”—is based on the assumption that the key to conscious processes can be found in the activities of these nerve cells. And in fact, the activities of the neurons and their communications with one another are central to many models of consciousness, such as those involving thalamocortical loops, synchronous 40 Hz oscillations, or the influence of the intralaminar thalamic nuclei on neuronal synchronization.

But there are also many theories that attempt to relate the functioning of human consciousness to structures at the molecular level, and even to the very strange effects of the quantum physics of the infinitely small. As scientific methods for investigating the infinitely small become more refined, more and more mechanisms will likely be discovered below the neuronal level, and it will be no surprise if some of these new mechanisms are indeed found to have an effect on human consciousness.

One molecule that may well play a role in the mechanisms of consciousness is the NMDA receptor. This large protein molecule takes the form of a channel passing through the neuronal membrane and serves as the binding site for glutamate, an excitatory neurotransmitter released into the synapses of a great many neurons. Once released into the synaptic gap, glutamate binds to the postsynaptic neuron’s NMDA receptor, causing this channel to open and thus initiating a whole series of biochemical reactions that make this synapse more efficient.

NMDA receptors thus act as critical components in the mechanism by which neurons form lasting associations by strengthening their connections with one another, thus creating what are known as neuronal assemblies. These assemblies occupy a prominent place in many neurobiological models of consciousness, so it seems entirely reasonable to assign the NMDA receptor molecule a significant role in the conscious processes of the human brain.

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